Filtration system utilizing a single valve to direct fluid streams between filter assemblies and corresponding methods

ABSTRACT

A filtration assembly for filtering polymer fluids at varying flow rates includes at least two filter housing assemblies releasably attached to a filter support or main block. Polymer fluid is delivered to the filter housing assemblies via an inlet passage in the main block, and filtered polymer fluid is transported from the filter housing assemblies to an outlet passage in the main block. One end of each filter housing assembly is attached to the main block and includes an inlet port for receiving polymer fluid from the inlet passage and an outlet port for delivering filtered polymer fluid to the outlet passage. A single valve disposed on the main block selectively alternates fluid flow between the main block and each filter housing assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from U.S. Provisional PatentApplication Serial No. 60/218,810, entitled “Polymer Filter,” filed Jul.18, 2000. The disclosure of this provisional patent application isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to purification and filtration ofpolymeric materials and, more particularly, to an improved method andapparatus for diverting flow of polymeric materials between at least twofilter housing assemblies utilizing a single valve in a continuouspolymer extrusion process.

[0004] 2. Description of the Related Art

[0005] In processes involving extrusion of molten thermoplastic polymerssuch as polyethylene, Nylon, polyester, polystyrene, etc., it isnecessary to filter foreign matter, e.g., contaminants and impurities,from the molten polymer. Two common examples of articles manufactured bymolten polymer are synthetic textile fibers and thin plastic films ofthe type used in packaging or for tapes (e.g., computer tape, soundrecording tape, etc.). In the production of synthetic textile fibers,which may have a final diameter of as little as ten microns, a particleof foreign matter of five or more microns diameter is quite likely tocause breakage of the fiber during manufacturing. It is desirable,therefore, to filter out any foreign material above a certain size.

[0006] In the manufacture of polymers for use in fiber production, afinal step is often a pelletizing operation where a filter is used toremove any impurities from the final pellets. One form of impurity is aso-called “gel”, a region in the molten polymer which has a much higherthan average viscosity due to excessive polymer molecular weight orcross-linking of polymer molecules. For some articles, such as very thinfilm and textile fibers, gels in the molten polymer degrade the productquality and are desirably removed by filtration, either at the time thepolymer is manufactured, or in-line in an extrusion process upstream offormation of the final product. It is further desirable to be able toreplace dirty filter media with clean filter media without interruptingan extrusion process and without introducing air to the molten polymerfluid stream, since air introduced to the stream causes bubbles in theextruded article, rendering the article defective. A polymer filterhaving the capability of changing media without interrupting theextrusion operation is generally called a “continuous polymer filter” or“continuous screen changer”.

[0007] Many polymer filtration systems are known in the art for removingimpurities from molten polymer. One common type of polymer filter is ascreen changer system. An example of a screen changer system isdescribed in U.S. Pat. No. 3,007,199 to Curtis, the disclosure of whichis incorporated herein by reference in its entirety. Screen changerstypically have a relatively small area of screen for a given flow rateof molten polymer. A filter area of one square inch of screen for flowrates of thirty to seventy pounds per hour of polymer is typical ofscreen changers. For instance, an extruder of 4.5 inches screw diameterat full production can melt 600 to 1100 pounds per hour of polymer andis commonly fitted with a screen changer using screens of 4.5 inchesdiameter or 15.9 square inches of filter area. This yields a flow rateof approximately thirty-eight to sixty-nine pounds per hour per squareinch of filter area. It would be very unusual but possible to use ascreen changer with screens bigger than eight inches diameter on a 4.5inch extruder. This would yield fifty square inches of area or twelve totwenty-two pounds per hour of polymer flow per square inch of filterarea. In any case, screen changers of this type are suitable to removedust, dirt, metal particles and pigment agglomerates down to a micronsize of about forty, more often one hundred microns.

[0008] Gel removal, on the other hand, requires filtration by mediahaving a micron rating of twenty or finer, and typically a greater“depth” or thickness of media is used than when merely removing dirt.Gels are amoeba-like in that they can change shape to pass throughnormal filter screens and then resume a more compact shape downstream ofthe screen. The combination of finer media and a greater thickness ofmedia tends to cause a very high pressure drop through the filter unlessa large area of filter media is used. For this reason, filters for gelremoval normally have one square inch of filter area for each 0.20 to0.70 pounds per hour of polymer flow. A filter used with a 3.5 inchdiameter screw extruder having a melt rate of 350 pounds/hour would havea filter media area of about 1300 square inches, or nine square feet.These large area filters are not only useful for molten polymer, butalso for solutions of polymer (so-called dopes). Polymer solutions (asused to make spandex or acrylic fibers) are lower in viscosity thanpolymer melts, so somewhat less filter area is needed to remove the gelsthat are common in these dopes. Also, filters for polymer solutionsoften operate at ambient temperature, making it unnecessary to heat thefilter apparatus.

[0009] While many varying types of screen changers and other small areapolymer filters exist, most large-area gel filters have a similarconstruction and utilize a candle filter system. A candle filter systemtypically has two or more filter housings and uses valves to directpolymer to and from the filter housings. Each housing typically containsmultiple candle-type filter elements. The candle filter element istypically a perforated tube covered by pleated screen wire in two ormore layers. The candle filter system is normally used for high polymerflow rate and/or very fine filtration systems. The size and number ofcandle filters are selected based upon the desired flow rate of polymerfluid to be processed. An example of a candle filter system is describedin U.S. Pat. No. 3,833,121 to Singleton et al., the disclosure of whichis incorporated herein by reference in its entirety. One popular candlesize is 1.38″ O.D. by 16″ long and has 1.2 to 1.4 square feet of area,or about 9 square feet (1300 square inches) for seven candles. Such afilter can be used with a polymer flow rate of two hundred to onethousand pounds per hour, or 0.20 to 0.77 pounds per hour per squareinch of area. This corresponds to the output of an extruder with a screwdiameter of 2.5 to 4.5 inches.

[0010] U.S. Pat. No. 5,462,653 to Hills, the disclosure of which isincorporated herein by reference in its entirety, discloses anothercandle filtration system utilizing a single housing to filter polymerfluid. Briefly, the Hills system includes a generally cylindricallyshaped housing with six candle-type filter assemblies arranged in pairsin a ring about a central valve and distribution system. A rotatablecontrol plate controls the valve and distribution system and can be setin various positions to allow polymer flow through all of the filterassemblies or to prevent flow through individual pairs of filterassemblies while the other assemblies remain on-stream, in order topermit removal or replacement of clogged or dirty filters. While thesystem of Hills is useful in diverting polymer flow through variouscandle filter assemblies within a particular housing, the system doesnot disclose any mechanism for maintaining continuous filtration ofpolymer fluid in the event the entire filter housing needs to gooff-stream for cleaning.

[0011] Many candle-type polymer filter systems maintain one of twofilter housings operable or on-stream while the other is cleaned,installed and heated to be ready to accept the polymer when the filtermedium in the on-stream housing becomes too dirty for continuedoperation. To switch housings, at least two valves are operatedsimultaneously (or nearly simultaneously) and polymer is introduced tothe clean housing while flow continues through the dirty housing. Anexample of such a candle-type filter system is the Fluid Dynamics CPFsystem, which is manufactured by USF Filtration & Separation, Inc. Thissystem has two filter housings and uses two sliding spool valves todirect the polymer flow to and from the filter housings. During normaloperation, one of the two filter housings is on-stream (i.e., moltenpolymer is flowing therethrough) while the other filter housing iscleaned, installed and heated to be ready to accept the polymer. Whenthe on-stream filter becomes too dirty for continued operation, spoolvalves of the system are set in motion in the following sequence: (1)the inlet valve of the clean filter housing is slightly opened while theoutlet valve of the clean filter housing remains closed to allow thepolymer fluid to enter and fill the clean housing; (2) the trapped airin the clean housing is purged through a bleed port until all air isvented from the clean housing; (3) after the clean housing is completelyfilled with molten polymer, the bleed port is closed and then the outletvalve of the clean housing is fully opened; and (4) the inlet valve ofthe clean housing is fully opened, after which the inlet and outletvalves of the dirty housing are completely closed. This completes theswitching of the polymer fluid from the dirty housing to the cleanhousing, and the filter of the dirty housing can then be removed forcleaning or replacement. While the clean housing is being filled, thefilter element in the dirty housing continues to provide uninterruptedprocess filtration.

[0012] One typical problem associated with typical candle filter systemsis the lack of uniformity in the heating of candle housings. Anotherproblem with candle filter systems, such as the CPF system describedabove, is the occurrence of excessive residence time for the polymer inthe filter housings if the unit is operated well below its maximum flowcapacity. Normally, the size of a polymer filtration system is chosen toprovide sufficient filtration for the polymer process system at itsmaximum flow rate. The area of the filter media elements utilized tofilter the polymer fluid will determine the polymer flow rate capacitysuitable for the filter system. Under certain operating conditions orfor certain processes, the process system maybe required to run at areduced capacity, for example, in a process system having multiplefunctions or in systems producing plural-component polymer products. Oneproblem resulting from running the process system at a reduced capacityor variable capacity is that the molten polymer remains within thefiltration system for a relatively long period of time (i.e., thepolymer has a high polymer “residence time”).

[0013] Excessive residence time and non-uniform residence time can causethermal degradation of the polymer, particularly when thermallysensitive polymers are used. For example, one type of synthetic fiberproducing apparatus produces fibers with two polymer components,so-called bicomponent fibers. Such a machine would have an extruder anda filter for each polymer. If the machine were making a common type ofbicomponent fiber with a core of one polymer and a sheath of another, itis desirable to be able to vary the percentage of sheath polymer for 10%to 60%, while the core would vary from 40 to 90%. In the case of thesheath, this is a 6 to 1 variation in polymer flow, causing excessivefilter residence time when a thin sheath is being produced. To solvethis problem, it is necessary to replace the filter housings with oneshaving less volume and fewer or shorter candle elements. Shorterelements require a shorter housing to reduce volume, but a shorterhousing is not practical on all existing filter assemblies because thetwo valves and the polymer piping connected to the valves is a fixeddistance apart and will only accommodate a housing of one specificlength.

[0014] U.S. Pat. No. 6,221,266 to Wilkie et al., the disclosure of whichis incorporated herein by reference in its entirety, discloses acontinuous polymer filtration system that solves the problem ofexcessive residence time that occurs with varying polymer flow rates.The system in Wilkie et al. includes at least three independentlycontrollable and removable filter housings that extend from a commoninlet passage to a common outlet passage. Each filter housing includes avalve at its inlet and another valve at its outlet that may be opened orclosed independently of the valves for the other housings. Bymanipulating various valves, the Wilkie et al. system is capable ofdiverting polymer fluid flow through different filter housings of thefiltration system to effectively reduce excessive residence time whenpolymer flow rates change.

[0015] The Wilkie et al. system is similar to the CPF system and manyother candle filter systems employing multiple filter housings in thatmultiple valves are utilized to control fluid flow within the system.The utilization of multiple valves to divert polymer fluid streams fromone filter housing to another can be complicated. For example, operatorerror in switching polymer fluid flow between housings can cause polymerflow to be completely shut off to all housings, which stops flow fromthe extruder that delivers polymer to the filter system and causes asafety rupture disc typically installed at the exit of an extruder torupture. In such situations, the entire process must be halted until therupture disc is replaced.

[0016] Thus, it is desirable to provide a polymer filtration systemcapable of continuously filtering polymer streams at varying flow ratesto filter housings while maintaining a desired polymer residence timewithin the filter housings. It is further desirable to minimize the riskof operator error and damage to the system when diverting polymer fluidstreams between two or more filter housings.

SUMMARY OF THE INVENTION

[0017] It is an object of the present invention to reduce the complexityand manufacturing costs associated with diverting polymer fluid betweenfilter housing assemblies during a continuous filtration process.

[0018] Another object of the present invention is to provide afiltration system that prevents complete valve cut-off of polymer flowthrough the filtration system thereby preventing any damage orinterruption of polymer fluid flow within the system.

[0019] Yet another object of the present invention is to provide afilter system capable of filtering polymer fluids at various fluid flowrates while maintaining a desired polymer residence time within thefilter housing assemblies of the filter system.

[0020] A further object of the present invention is to provide easilyinterchangeable filter housing assemblies having varying volumes andfilter media areas to accommodate varying polymer flow rates through afilter system.

[0021] A still further object of the present invention is to maintainuniform heating of polymer fluid when directed through filter housingassemblies of a filtration system.

[0022] The aforesaid objects are achieved individually and incombination, and it is not intended that the present invention beconstrued as requiring two or more of the objects to be combined unlessexpressly required by the claims attached hereto.

[0023] According to the present invention, a polymer filtration systemincludes at least two filter housing assemblies in communication with aninlet passage that delivers polymer fluid into the system and an outletpassage transporting polymer fluid filtered by one of the filter housingassemblies out of the system. Each filter housing assembly includes oneor more filter media elements. A single valve is manipulated toselectively divert polymer fluid from one filter housing assembly to theother. Each filter housing assembly has an inlet port and an outlet portdisposed at one end of the assembly for receiving polymer fluid from theinlet passage and delivering filtered polymer fluid to the outletpassage via the valve. The filter housing assemblies are releasablysecured to a surface of a filter support with their inlet and outletports adjacent the surface of the filter support, while the valve isdisposed on an opposing surface of the filter support. The valve ensuresthat only one of the first and second filter housing assemblies receivespolymer fluid from the inlet passage and delivers filtered polymer fluidto the outlet passage at a single time. The system permits thecontinuous filtering of polymer material by utilizing one of the firstand second filter housing assemblies until cleaning is required. At suchtime, the valve diverts polymer fluid flow to the other of the first andsecond filter housing assemblies so that the first housing may becleaned.

[0024] The system further facilitates the use of filter housingassemblies of varying sizes and shapes to accommodate varying polymerfluid flow rates while maintaining a desired fluid residence time withineach housing. Since the inlet and outlet ports are located at the sameend on each filter housing assembly, the lengths of filter housingassemblies may be easily modified to accommodate filter media (e.g.,candle filters) of varying sizes without the need for modifying any ofthe other elements of the system, such as the filter support and valve.Additionally, each filter housing assembly may be easily equipped withsuitable heating elements to maintain a desired uniform temperature ofpolymer fluid flowing through the assembly. The heating elements arefurther adaptable to accommodate varying filter housing assembly sizes.

[0025] The above and still further objects, features and advantages ofthe present invention will become apparent upon consideration of thefollowing detailed description of a specific embodiment thereof,particularly when taken in conjunction with the accompanying drawingswherein like reference numerals in the various figures are utilized todesignate like components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is an exploded perspective view in partial section of apolymer filtration system utilizing a pair of filter assemblies inaccordance with an exemplary embodiment of the present invention.

[0027]FIG. 2 is a front elevational view in partial section of thefiltration system of FIG. 1.

[0028]FIG. 3 is side elevational view in section of the filtrationsystem of FIG. 1 taken along lines III-III of FIG. 2.

[0029]FIG. 4 is a top plan view in partial section of a filter housingassembly of the polymer filtration system of FIG. 1.

[0030]FIGS. 5, 7 and 9 are broken front elevational views in section ofthe filtration system of FIG. 1 taken along lines V-V of FIG. 3, whereinthe valve is positioned at varying locations on the main block of thesystem.

[0031]FIGS. 6, 8 and 10 are broken front elevational views in section ofthe filtration system of FIG. 1 taken along lines VI-VI of FIG. 3,wherein the valve is positioned at varying locations on the main blockof the system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] In accordance with the present invention, a filtration system forfiltering molten or solution polymer fluid streams includes at least twofilter housing assemblies which extend from a single valve assembly thatselectively provides fluid flow to at least one filter housing assembly.Each filter housing assembly typically includes one or more filter mediaelements that filter the fluid passing through the assembly. The filterhousing assemblies may vary with respect to each other in size andnumber of filter media elements depending upon the residence timedesired for polymer fluid flowing through a particular assembly. Theindividual controllability of the size and configuration of each filterhousing assembly allows the polymer throughput capacity of thefiltration system to be adjusted in accordance with the type of fiberprocessing system implemented (e.g., bicomponent fiber production,sheath-core fiber production, etc.).

[0033] An exemplary embodiment of a continuous filtration system inaccordance with the present invention is illustrated in FIGS. 1-10.Referring to FIG. 1, filtration system 1 includes a filter supportstructure in the form of a generally rectangular main block 10, a pairof generally cylindrical filter housing assemblies 40, 40′ and a valveassembly connected to the main block. Unless indicated otherwise,components of the filtration system are typically constructed of asuitably rigid material (e.g., steel). In particular, the main block andcomponents of the valve assembly are typically constructed of hardanti-galling and corrosion-resistant steel to facilitate smooth andrelatively easy operation of the valve assembly as described below.

[0034] Main block 10 includes a lower surface 12 and an opposing uppersurface 14, a front surface 15 and an opposing rear surface 16, and twoopposing side surfaces 17, 18. The front and rear surfaces typicallyhave a smaller surface area in comparison to the upper and lowersurfaces, and the side surfaces typically have a smaller surface area incomparison to the front and rear surfaces. It is to be understood thatthe terms “upper”, “lower”, “front”, “rear”, “side”, “horizontal”,“vertical”, “bottom”, “upper”, “lower”, “length”, “width” and the likeare used herein merely to describe points of reference and do not limitthe present invention to any specific orientation or configuration.

[0035] An inlet pipe 2 is connected to front surface 15 of the mainblock and is in fluid communication with an inlet passage 20 extendingfrom the main block front surface into the main block. A flange 3extends radially from the end of inlet pipe 2 adjacent the main blockfront surface. The flange secures the inlet pipe to the front surface ofthe main block via bolts 4 extending through the flange into the mainblock thereby ensuring a fluid tight relationship between the inlet pipeand the inlet passage of the main block. The inlet pipe delivers polymerto the main block for filtering by the system. Inlet passage 20 extendstransversely from the main block front surface to an interior portionwithin the main block. At that interior portion, inlet passage 20 bendsat an elbow, changing direction to extend transversely with respect tbthe main block upper and lower surfaces (i.e., vertically upward asshown in FIG. 1) and ultimately emerge at aperture 21 on upper surface14 of the main block. An outlet passage 22 (see FIGS. 6, 8 and 10)extends from an aperture 23 on upper surface 14 of the main block torear surface 16 of the main block in a substantially similar manner asinlet passage 20. The inlet and outlet apertures 21, 23 are typicallyaligned linearly with respect to each other in a direction transversethe longitudinal direction of the main block upper surface. An outletpipe 5 is secured in a fluid tight relationship to the main block rearsurface with a flange 6 and bolts 7. The outlet pipe is in fluidcommunication with outlet passage 22 and receives filtered polymer fluidfrom the main block for further processing.

[0036] Referring to FIGS. 2 and 3, a pair of filter input channels 30,31 extend within main block 10 between the main block upper and lowersurfaces. Each filter input channel delivers polymer fluid from inletpassage 20 in the main block to a corresponding filter housing assemblyas described below. Each filter input channel 30, 31 forms an elongatedaperture 32, 33 on the main block upper surface. Elongated apertures 32,33 are essentially slot-shaped openings having a generally “race track”geometry with the longer or longitudinal dimension of each apertureextending in the longitudinal direction of the main block upper surfaceand the transverse edges being rounded. Elongated apertures 32, 33 arefurther separated a suitable distance from each other in thelongitudinal direction of the main block upper surface, with aperture 21of inlet passage 20 disposed therebetween such that all three apertures21, 32, 33 are in substantial linear alignment with each other in thelongitudinal direction. Each filter input channel 30, 31 also forms agenerally circular aperture on the main block lower surface. The filterinput channels are angled to extend away from each other in a downwarddirection within the main block such that the channel apertures on themain block lower surface have a greater spacing in comparison to thespacing between the elongated channel apertures on the main block uppersurface. The filter input channel apertures on the main block lowersurface are suitably spaced from each other to facilitate alignment ofinlet bores on filter housing assemblies with such apertures asdescribed below.

[0037] A pair of filter output channels 34, 35 (see FIGS. 6, 8 and 10)extend in a substantially similar manner in main block 10 as filterinput channels 30, 31 to deliver filtered polymer fluid from the filterhousing assemblies to outlet passage 22 in the main block. Specifically,each of the filter output channels 34, 35 extends between the main blockupper and lower surfaces, forming an elongated aperture 36, 37 on themain block upper surface and a generally circular aperture on the mainblock lower surface. The elongated apertures 36, 37 of filter outputchannels 34, 35 are essentially slot-shaped openings having a generally“race track” geometry with the longer or longitudinal dimension of eachelongated aperture extending in the longitudinal direction of the mainblock upper surface and the transverse edges being rounded. Elongatedapertures 36, 37 are separated a suitable distance from each other inthe longitudinal direction of the main block upper surface with aperture23 of outlet passage 22 disposed therebetween such that all threeapertures 23, 36, 37 are in substantial linear alignment with each otherin the longitudinal direction. Filter output channels 34, 35 extend awayfrom each other in the downward direction within the main block and in asubstantially similar manner as filter input channels 31, 32 such thatthe filter output channel apertures on the main block lower surface havea greater spacing in comparison to the spacing between the filter outputchannel elongated apertures on the main block upper surface. The filteroutput channels apertures on the main block lower surface are furthersuitably spaced from each other to facilitate appropriate alignment ofoutlet bores on filter housing assemblies with such apertures asdescribed below.

[0038] The apertures are aligned on the main block upper surface suchthat a filter input channel elongated aperture 32, 33 is aligned with arespective filter output channel elongated aperture 36, 37 in adirection transverse the longitudinal direction of the main block uppersurface. Additionally, the inlet passage aperture 21 is aligned with theoutlet passage aperture 23 in the direction transverse the longitudinaldirection of the main block upper surface. For reasons that will beexplained below, the longitudinal dimensions of elongated apertures 36,37 of filter output channels 34, 35 are preferably smaller than thelongitudinal dimensions of elongated apertures 32, 33 of filter inputchannels 30, 31.

[0039] Electrical heating elements are disposed within the main block toheat the main block to a desired temperature. Specifically, heatingchannels 38 formed within main block 10 extend between side surfaces 17,18 of the main block and are suitably dimensioned to receive heatingrods 39. The heating rods include wiring connecting to a controller (notshown) for controlling the heating of the rods and thus the temperatureof the main block. It is noted that any number of heating elements maybe disposed at any locations on or in the main block to maintain themain block at a desired temperature.

[0040] Referring again to FIG. 2, filter housing assemblies 40, 40′ ofthe filtration system include a plurality of filter media elements forfiltering polymer fluid streams. Although both filter housing assembliesare substantially similar in size and configuration in the illustratedembodiment, it is noted that filter housing assemblies utilized in thepresent invention may vary in size, shape, number of filter mediaelements, etc. depending upon the desired flow rate capacity through aparticular filter housing assembly for a particular process. Each filterhousing assembly 40, 40′ includes a housing head secured to a generallycylindrical hollow housing 41 having a chamber 42 disposed therein. Thehousing head is formed by a generally circular upper plate 44 attachedto a generally circular lower plate 45. Lower plate 45 attaches to anupper portion of housing 41. Upper and lower plates 44, 45 may beconnected in any suitable manner that ensures a fluid-tight relationshipbetween the plates. For example, the plates may be brazed together orbolted together with a flat gasket sandwiched between their adjacentsurfaces. Alternatively, the housing head may include a single circularplate having the combined features of the upper and lower plates. Thehousing head is secured to housing 41 in a fluid tight relationship viaa plurality of bolts 46 extending through both plates 44, 45 andthreadably engaging with a flange 43 extending radially from the upperportion of the housing (see FIGS. 1 and 2). Each filter housing assembly40, 40′ is secured to lower surface 12 of the main block with two pairsof bolts 24. Specifically, the two pairs of bolts 24 extend through themain block upper and lower surfaces via bore holes 25 and engage withcorresponding threaded apertures 48 on an upper surface of each filterhousing assembly upper plate 44 to secure each filter housing assemblyto a portion of the main block lower surface.

[0041] Upper plate 44 of each filter housing assembly 40, 40′ includes agenerally circular inlet bore 50 and a generally circular outlet bore52. Inlet bore 50 is typically located at or near the center of theupper plate so as to be concentrically aligned and in fluidcommunication with the aperture formed by one of the filter inputchannels 30, 31 on the main block lower surface when each filter housingassembly is bolted to the main block. Outlet bore 52 is offset frominlet bore 50 and is positioned to be concentrically aligned and influid communication with the aperture formed by one of the filter outputchannels 34, 35 on the main block lower surface upon connection of eachassembly to the main block. A metal seal 53 disposed within inlet bore50 near the upper surface of upper plate 44 prevents any leakage betweenthe upper plate and the main block lower surface as polymer fluidtravels from a corresponding filter input channel 30, 31 of the mainblock to inlet bore 50. Similarly, a metal seal 55 is disposed withinoutlet bore 52 near the upper surface of upper plate 44 to preventleakage of filtered polymer fluid traveling from the outlet bore to acorresponding output channel 34, 35 of the main block. The upper plateinlet bore is in concentric alignment and fluid communication with acentral bore 54 extending through lower plate 45, which is in turn inconcentric alignment and fluid communication with a generallycylindrical hollow pipe 56 extending within housing chamber 42. Hollowpipe 56 extends substantially the entire length of the housing chamberand terminates at a pipe outlet 57 near a bottom portion of the housingchamber. The travel path of polymer fluid within each filter housingassembly 40, 40′ is depicted by arrows in FIGS. 2 and 3. Specifically,polymer fluid enters each filter housing assembly 40, 40′ by passingfrom a corresponding filter input channel 30, 31 into concentricallyaligned inlet bore 50 of upper plate 44. The polymer fluid continues totravel from the upper plate inlet bore through central bore 54 of lowerplate 45 and into pipe 56, where the fluid exits through pipe outlet 57at the bottom portion of housing chamber 42.

[0042] A plurality of filter media elements are disposed around pipe 56.The filter media elements are typically candle filters 60 that aregenerally cylindrical, perforated and hollow and that extendsubstantially the entire length of the housing chamber. Screen wire 62surrounds each candle filter 60 and is typically pleated as indicated inFIGS. 1 and 4. It is noted that the screen wire is not depicted in FIGS.2 and 3 to simplify the view and clearly show the fluid travel pathwithin the filter housing assembly. In the embodiment depicted in thedrawings, each filter housing assembly 40, 40′ includes five candlefilters 60 disposed in an array around pipe 56 within housing chamber42. In general, any number of candle filters or other filter mediaelements (e.g., one filter media element) may be utilized, and theinvention is not limited to the illustrated configuration of filterelements. Polymer fluid exiting pipe outlet 57 proceeds to travel withinthe housing chamber through pleated screen wire 62 and into candlefilters 60 at varying locations along each candle filter, as indicatedby the arrows in FIGS. 2 and 3. Upon passing through the screen wire andentering the hollow portion of a corresponding candle filter, thepolymer fluid is filtered and continues traveling within the candlefilter hollow portion toward the housing head. Since the pressure dropthrough the screen wire is high and the pressure drop due to flow insidethe housing chamber is low, polymer fluid will tend to flow nearlyequally through all areas of the surface of all the candle filters.

[0043] It is noted that each filter housing assembly is functionalwithout a pipe to deliver polymer fluid from the housing head to abottom portion of the housing chamber. However, without the pipe,polymer flow rates into the housing chamber from the inlet bore in thehousing head would become too slow as the polymer approached the ends ofthe candle filters near the bottom of the housing chamber. The slowflowing polymer fluid would create a region of stagnant polymer subjectto thermal degradation near the bottom portion of the housing chamber.Thus, the pipe in each filter housing assembly conveys all of theincoming polymer fluid to the bottom end of the housing, avoidingexcessively slow polymer flow near the bottom end of the candle filtersand avoiding any stagnant regions.

[0044] Each filter media element is typically secured at an upper end tolower plate 45 within each filter housing assembly. As indicated inFIGS. 2 and 3, lower plate 45 includes an array of threaded candleholder bores 64, each aligned to engage with a threaded upper end of acorresponding candle filter 60. All of the candle holder bores arefurther aligned and in fluid communication with a ring cavity 66disposed on the surface of upper plate 44 that is adjacent lower plate45. The ring cavity forms an annular channel on the surface of the upperplate that does not extend to the opposing surface of the upper plate(i.e., the surface adjacent the main block lower surface). Each of theupper ends of candle filters 60 includes a candle outlet aperture 67(FIG. 4) that is aligned and in fluid communication with the ringcavity. A portion of ring cavity 66 is further aligned and in fluidcommunication with outlet bore 52 of the upper plate. Thus, filteredpolymer fluid traveling through each candle filter 60 will exit candleoutlet aperture 67 and proceed into ring cavity 66 of the upper plate.The filtered polymer fluid will then continue to travel within ringcavity 66 until reaching upper plate outlet bore 52, where the filteredpolymer fluid then passes through the upper plate outlet bore and into acorresponding, filter output channel 34, 35 within main block 10.

[0045] Each filter housing assembly also includes a bleed line forremoving unwanted air from the filter housing chamber prior to allowingfiltered polymer fluid to travel beyond the main block. Specifically,the bleed line includes a bleed passage 68 extending from a portion ofring cavity 66 within upper plate 45 to an exposed portion of thecylindrical outer surface of the upper plate (see FIGS. 1 and 3). Ableed plug 69 extends from the exposed portion of the upper plate and isremovably secured (e.g., via threaded or other engagement) in a fluidtight relationship with bleed passage 68. During initial use of eitherfilter housing assembly 40, 40′, polymer fluid is allowed to enter thefilter housing chamber from the main block as described above, butprevented from leaving the main block, by adjusting the valve assemblyin a manner described below, until substantially all the air within thefilter housing chamber is forced out through the bleed line.Specifically, bleed plug 69 is disengaged from bleed passage 68 asufficient amount to open the bleed line and allow polymer fluidentrained with air to exit the filter housing assembly via the bleedpassage. When polymer fluid exiting the filter housing assembly via thebleed passage is determined to be free of bubbles (i.e., indicative ofall air being evacuated from the filter housing chamber), the bleed plugis appropriately secured within the bleed passage to re-establish afluid tight relationship. Polymer fluid is then permitted to pass fromthe main block via a filter output channel 34, 35 by adjusting the valveassembly as described below.

[0046] A generally cylindrical heating jacket 70 surrounds each filterhousing assembly to maintain the temperature of polymer fluid within thefilter housing chambers. The heating jacket is constructed of a goodheat conducting material (e.g., aluminum) and may further be surroundedby insulation (not shown) to reduce heat loss from the filter housingassembly. Concentric band heaters 71 are wrapped around the heatingjackets and secured thereto with brackets 73, and each heating jacket isremovably secured to a corresponding filter housing assembly via a bolt74 attaching the bottom surface of the heating jacket to filter housing41. A temperature sensor 72 (e.g., a thermocouple) extends throughheating jacket 70 and is positioned in close proximity to filter housing41. Electrical power is supplied to band heaters 71 and typicallycontrolled by a remote temperature controller (not shown) based upontemperature signals the temperature controller receives from temperaturesensor 72. Thus, the temperature within a filter housing chamber may beprecisely maintained at a desired temperature during use of the filterhousing assembly.

[0047] The valve assembly for system 1 utilizes a single valve toselectively divert polymer fluid flow from at least one filter housingassembly to another. Referring again to FIG. 1, the valve assemblyincludes a generally rectangular slide valve 80 disposed adjacent uppersurface 14 of main block 10 between a pair of generally rectangularrails 82. The slide valve and rails each have a longer dimensionextending in the longitudinal direction of the main block upper surface.A generally rectangular valve cap 84 overlies the slide valve and railsand secures the slide valve between the rails and between the valve capand the main block upper surface. Heating channels 90 extendlongitudinally within and between opposing side surfaces of the valvecap. The heating channels are suitably dimensioned to receive heatingrods 91. The heating rods include wiring that typically connect to acontroller (not shown) for controlling heating of the rods and thus thetemperature of the valve cap. It is noted that any number of heatingelements may be disposed at any locations on or in the valve cap tomaintain the valve cap at a desired temperature. It is further notedthat the controller utilized for heating the valve cap may be the samecontroller utilized for heating the main block and/or the filter housingassemblies.

[0048] Valve cap 84 includes two sets of bore holes 85 positionedlongitudinally along the edges of the valve cap that extend beyond theshorter dimension of slide valve 80 when the valve cap is positionedover the slide valve. Bore holes 85 extend through the valve cap betweenthe valve cap upper and lower surfaces and are concentrically alignedwith corresponding bore holes 87 extending through rails 82 and two setsof longitudinally aligned threaded apertures 88 disposed on the mainblock upper surface. A plurality of bolts 86 extend through the boreholes on the valve cap and rails and threadingly engage with thethreaded apertures on the main block upper surface to secure the valvecap and rails to the main block upper surface. The two sets of threadedapertures on the main block are suitably spaced from each other toprovide a snug fit for the slide valve when the rails are bolted to themain block upper surface while permitting movement of the slide valvebetween the rails in the longitudinal direction of the main block. Theslide valve and rails are also typically dimensioned to be substantiallyflush at their surfaces facing the valve cap and the main block uppersurface when secured to the main block so as to ensure a fluid tightrelationship between the slide valve and the main block during operationof the valve assembly. One skilled in the art will recognize that thedegree of tightening of bolts 86 as well as the dimensions of slidevalve 80, rails 82 and/or valve cap 84 can be adjusted within selectedtolerances to facilitate a desired frictional resistance to movement ofthe slide valve between the rails, valve cap and main block uppersurface while maintaining a fluid tight relationship between the slidevalve and the main block. An eyelet 89 or similar connector is affixedat a longitudinal end of the slide valve to permit attachment of theslide valve to a mechanical (e.g., hydraulic or screw-type) device forfacilitating movement of the slide valve. The mechanical device may beautomated or manually operated.

[0049] Slide valve 80 includes a pair of elongated pockets or grooves100, 102 disposed and longitudinally oriented on the surface of theslide valve adjacent upper surface 14 of main block 10. Groove 100 isappropriately aligned on the slide valve surface to correspond withlinearly aligned apertures 21, 32, 33 of inlet passage 20 and filterinput channels 30, 31, respectively, on the main block upper surfacewhen the slide is received between the rails. Similarly, groove 102 isappropriately aligned on the slide valve surface to correspond withlinearly aligned apertures 23, 36, 37 of outlet passage 22 and filteroutput channels 34, 35, respectively, on the main block upper surfacewhen the slide valve is received between the rails. The dimensionsand/or positioning of each groove are further selected such that onlytwo immediately neighboring apertures in a linear alignment of aperturesare in fluid communication with a corresponding groove at selectedpositions of the slide valve on the main block upper surface.

[0050] The positioning of slide valve 80 at varying locations along themain block upper surface so as to align grooves 100, 102 with selectedapertures is illustrated in FIGS. 5-10. It is initially noted that FIGS.5, 7 and 9 illustrate a cross-sectional view of system 1 taken alonglines V-V of FIG. 3, whereas FIGS. 6, 8 and 10 illustrate across-sectional view of the system taken along lines VI-VI of FIG. 3.For the purpose of simplicity, the valve cap is not shown in any ofFIGS. 5-10. As depicted in FIGS. 5 and 6, slide valve 80 maybepositioned along main block upper surface 14 such that groove 100 of theslide valve is aligned and in fluid communication only with aperture 21of inlet passage and aperture 32 of filter input channel 30 on the mainblock, and groove 102 of the slide valve is aligned and in fluidcommunication only with aperture 23 of outlet passage 22 and aperture 36of filter output channel 34 on the main block. The valve position ofFIGS. 5 and 6 allows polymer fluid to flow into and out of filterhousing assembly 40 but prevents any flow of polymer fluid into or outof filter housing assembly 40′. The slide valve may also be positionedas depicted in FIGS. 9 and 10, wherein groove 100 is aligned and influid communication only with aperture 21 of inlet passage 20 andaperture 33 of filter input channel 31, and groove 102 of the slidevalve is aligned and in fluid communication only with aperture 23 ofoutlet passage 22 and aperture 37 of filter output channel 35. The valveposition of FIGS. 9′ and 10 allows polymer fluid to flow into and out offilter housing assembly 40′ but prevents any flow of polymer fluid intoor out of filter housing assembly 40. Thus, the slide valve can beselectively positioned to control flow of polymer fluid exclusivelythrough one of the two filter housing assemblies. Further, the slidevalve can be easily repositioned on the main block upper surface (e.g.,by sliding the slide valve in the direction of arrow 110) to divertpolymer fluid flow from one filter housing assembly (e.g., assembly 40)to another (e.g., assembly 40′).

[0051] As previously noted, the longitudinal dimensions of apertures 36,37 of filter output channels 34, 35 are typically smaller than thelongitudinal dimensions of apertures 32, 33 of filter input channels 30,31. Dimensioning of apertures 36, 37 in such a manner providesadditional fluid control positions for the valve. Specifically, thevalve may be adjusted to an intermediate position wherein groove 100 isin fluid communication with all three apertures 21, 32, 33 of inletpassage 20 and filter input channels 30, 31, respectively, whereasgroove 102 is in fluid communication only with aperture 23 of outletpassage and one of apertures 36, 37 of filter output channels 34, 35,respectively. An example of one such intermediate position is depictedin FIGS. 7 and 8. Specifically, slide valve 80 is positioned along mainblock upper surface 14 such that groove 100 is in fluid communicationwith all three apertures 21, 32, 33 (FIG. 7), whereas groove 102 is influid communication only with apertures 23, 36 (FIG. 8). Thus, the valveconfiguration depicted in FIGS. 7 and 8 for system 1 allows polymerfluid entering the main block from inlet pipe 2 to travel from inletpassage 20 to both filter input channels 30, 31 and enter both filterhousing assemblies 40, 40′ at the same time. However, while filteredpolymer fluid is allowed to pass from one filter housing assembly 40into outlet passage 22 via filter output channel 34, the other filterhousing assembly 40′ is prevented from delivering filtered polymer fluidto outlet passage 22 because its corresponding filter output channel 35is not in fluid communication with the outlet passage in the main block.The slide valve may be further adjusted in the direction of arrow 110 sothat groove 100 is still in fluid communication with all three apertures21, 32, 33, but now groove 102 is in fluid communication only withapertures 23, 37. In other words, in such a position the slide valvepermits filtered polymer fluid to leave filter housing assembly 40′ viafilter output channel 35 but prevents filtered polymer fluid fromleaving filter housing assembly 40 via filter output channel 34. Thisfeature of the present invention permits air to be removed from anyfilter housing assembly during its initial use, utilizing its bleed lineas described above, while preventing filtered polymer fluid from leavingthat filter housing assembly. Once it has been established that thefiltered housing assembly is free of entrapped air (i.e., polymer fluidexiting the bleed line is free of bubbles), the slide valve, may beshifted into suitable alignment as described above to allow filteredpolymer fluid to exit the filter housing assembly.

[0052] The valve assembly may further include a valve location indicatorto indicate the flow of polymer fluid through the filter housingassemblies based upon the position of the valve as described above. Forexample, in situations where the slide valve is manually operated,indicia (e.g., an arrow) that corresponds to the longitudinal positionof the slide valve on the main block upper surface may be aligned withother indicia (e.g., bars on a linear scale) to provide an indication asto the precise position of the slide valve grooves with respect to theapertures on the main block. Alternatively, an electronic positionindicator may be implemented. An electronic position indicator isparticularly suitable in situations where the slide valve is automated.

[0053] Operation of system 1 will now be described with the valveassembly initially positioned to direct flow exclusively into and out offilter housing assembly 40 (i.e., the slide valve position depicted inFIGS. 5 and 6). Slide valve 80 is positioned on the main block uppersurface such that groove 100 is aligned and in fluid communication onlywith aperture 21 of inlet passage 20 and aperture 32 of filter inputchannel 30 of the main block. Similarly, groove 102 is aligned and influid communication only with aperture 23 of outlet passage 22 andaperture 36 of filter output channel 34 of the main block. Duringoperation, main block 10, valve cap 84 and housing assembly 40 aretypically heated to a desired temperature prior to directing polymerfluid through system 1. Each of the main block, valve cap and housingassembly may be heated via their respective heating rods or heatingjacket. Upon achieving a desired temperature, polymer fluid is deliveredunder pressure by inlet pipe 2 into inlet passage 20 at front surface 15of main block 10. Polymer fluid travels through inlet passage 20 andexits aperture 21 at upper surface 14 of the main block, passes throughgroove 100 of slide valve 80 and into filter input channel 30 viaaperture 32 on the main block upper surface. Filter input channel 30delivers the pressurized polymer fluid to the housing head of filterhousing assembly 40, where the polymer fluid passes from the main blockthrough inlet bore 50 of upper plate 44 and central bore 54 of lowerplate 45 to enter hollow pipe 56 within housing chamber 42 of filterhousing assembly 40. The polymer fluid is filtered by traveling throughcandle filters 60 within the housing chamber in the manner describedabove. The filtered polymer fluid exits each candle filter 60 via candleoutlet aperture 67 and enters ring cavity 66 in upper plate 44. The ringcavity directs the flow of filtered polymer fluid into outlet bore 52 ofthe upper plate, which in turn leads to filter output channel 34 in themain block. The filtered polymer fluid travels through filter outputchannel 34 and emerges from aperture 36 into groove 102 in the slidevalve. Groove 102 directs filtered polymer fluid into outlet passage 22via aperture 23 on the main block upper surface, and the filteredpolymer fluid travels through the outlet passage and exits the mainblock at its rear surface 16. The filtered polymer fluid enters outletpipe 5 and is carried away from the filtration system for furtherprocessing.

[0054] Once the candle filters within filter housing assembly 40 becomesufficiently clogged with material (e.g., dirt, impurities, gels, etc.)removed from polymer fluid streams passing through the walls of thefilters, polymer fluid flow may be diverted to filter housing assembly40′ to facilitate removal of filter housing assembly 40 for cleaning andreplacement of a new filter housing assembly on the main block. Filterhousing assembly 40′ is typically heated to the desired temperature,utilizing its heating jacket 70, temperature sensor 72 and a suitablecontroller, prior to diverting polymer fluid into the assembly. Slidevalve 80 is then shifted longitudinally along the main block uppersurface as described above from an initial position illustrated in FIGS.5 and 6 to an intermediate position illustrated in FIGS. 7 and 8. At theintermediate position (FIGS. 7 and 8), polymer fluid flows from groove100 of slide valve 80 into both filter input channels 30, 31 in mainblock 10 leading to both filter housing assemblies 40, 40′. However, theslide valve at such intermediate position permits filtered polymer fluidto leave only filter housing assembly 40 by passing into groove 102 ofthe slide valve via filter output channel 34 in the main block. Any airentrapped in housing chamber 42 of filter housing assembly 40′ can beevacuated via the bleed line for the assembly in a manner describedabove while the slide valve is in its intermediate position. Uponsufficient removal of air entrapped within filter housing assembly 40′,polymer fluid flow is completely diverted from filter housing assembly40 to filter housing assembly 40′ by further shifting slide valve 80 ina manner described above and illustrated in FIGS. 9 and 10. At suchvalve position, polymer fluid flows exclusively into and out of filterhousing assembly 40′, allowing filter housing assembly 40 to be removedfrom system 1 for cleaning.

[0055] The removal of filter housing assembly 40 is typicallyimplemented by disconnecting its heating jacket 70, including its bandheaters 71 and temperature sensor 72, from the controller. The bleedline for the assembly may be opened prior to removing the assembly fromthe main block to ensure that polymer fluid remaining in the filterhousing chamber is not under any significant pressure. Heating jacket 70may optionally be kept on the assembly to ensure the polymer remainsfairly hot and fluid within the filter housing chamber for easy removal.Alternatively, the heating jacket may be easily removed by disengagingbolt 74 from filter housing 41. Candle filters 60 within the filterhousing chamber may be removed and the filter housing and candle filtersmay be cleaned in any suitable manner (e.g., using a furnace, salt bath,boiling solvents, etc.).

[0056] During continued operation, a new filter housing assembly may beinstalled at the open location on main block 10. Upon accumulation of asufficient amount of filtered material from polymer fluid flowingthrough filter chamber 42 of filter housing assembly 40′, the slidevalve may be shifted to another intermediate valve position tofacilitate air evacuation of the new filter housing assembly, followedby further shifting of the slide valve to completely divert polymerfluid flow to the new filter housing assembly thereby facilitating theremoval and cleaning of filter housing assembly 40′.

[0057] Thus, the filtration system of the present invention is capableof continuous and uninterrupted operation by diverting fluid flowbetween filter housing assemblies with the manipulation of a singlevalve rather than multiple valves as is required in other systems withmultiple filter housing assemblies. Additionally, the system alwaysmaintains polymer flow through at least one filter housing assemblyduring operation of the valve, thereby eliminating any possibility ofpressure buildup and extruder damage caused by operator error whenadjusting the valve.

[0058] Furthermore, filter housing assemblies having differing flow ratecapacities maybe easily replaced within the system depending upon theflow requirements for a particular process. In most applications, thelongest candle that would normally be used would have a length about 15times its diameter. For example, a candle filter with a diameter ofabout 2 inches would typically have a length no longer than about 30inches. Such a candle with pleated screens would have a screen area ofabout 5 square feet or 720 square inches. Assuming a reduction to 20% ofthe area was required due to a decrease in flow rate for polymer to beprocessed, the 2 inch diameter candle could be reduced to about 6 inchesin length. The filter housing assembly of the present invention could beeasily modified to retain candle filters or other filter media ofvarying sizes while still being suitable for use with the system.

[0059] Modification of the filter housing assembly may be easilyaccomplished by separating the hollow housing portion from the housinghead and replacing that housing with a new housing having a reduced size(e.g., length) to accommodate a desired volume of fluid to be filtered.The new housing including smaller sized candle filters may be attachedto the housing head and the filter housing assembly reconnected to themain block. The heating jacket surrounding the housing may also beremoved and reattached to the new housing with the same bolt or a longerbolt depending upon the size of the new housing. Thus, the filtrationsystem of the present invention with the single valve assembly andhousing head design facilitates simple, convenient and economicmodification of fluid filtration capacity by replacement of therelatively inexpensive housing portion of the filter housing assemblywithout any modification to the relatively expensive housing headportion. Additionally, the system design allows a single heating jacketto be utilized for a variety of filter housing assembly sizes. Incontrast, conventional continuous filtration systems employing multiplevalves typically utilize filter housing assemblies with a housing headat each end that secures to a valve. Those conventional systems requiretheir filter housing assemblies to be of a specific length so that eachhousing head may appropriately align with a valve disposed at a fixedlocation within the system. Modification of the size of filter housingassemblies in those systems would require a significant modification tothe system itself.

[0060] It is to be understood that the embodiments described above andillustrated in the drawings represent only a few of the many ways ofimplementing a filtration system utilizing a single valve to directfluid streams between filter housing assemblies.

[0061] The filter housing assemblies may be made of any suitablematerials and may have any suitable configuration rendering a desirablefluid flow capacity for a particular polymer process. It is noted thatthe system has been described and displayed with two filter housingassemblies for illustrative purposes only, and the filtration system ofthe present invention may utilize any number of filter housingassemblies. For example, a system contemplated by the present inventionmay include any number of pairs of filter housing assembliesappropriately aligned with a single valve such that manipulation of thevalve effects a diverting of polymer fluid from one filter housingassembly to another in each pair. In another example, the system mayinclude a linear array of filter housing assemblies disposed inappropriate alignment with a single valve such that manipulation of thevalve effects a diverting of polymer fluid from one filter housingassembly to an adjacent filter housing assembly in the linear array. Inyet another example, the system may utilize a single valve to divertfluid flow between one filter housing assembly and two or more filterhousing assemblies. Additionally, the filter housing assemblies may beoriented in any suitable manner (e.g., horizontally, vertically, etc.)with respect to the filter support structure and may be aligned in anysuitable relationship (e.g., parallel or non-parallel alignment) withrespect to each other. The filter housing assemblies may be of varyingsizes and/or may have filter media elements with varying surface areasto accommodate varying polymer flow rates while maintaining suitableresidence time of polymer fluid within the assemblies. The filter mediaelements may be candle filters or any other suitable filter. Further,each filter housing assembly may include any number of filter mediaelements (e.g., one filter media element). The bleed line for eachfilter housing assembly may have any suitable configuration to allow theflow of fluid from the housing chamber of an assembly. The bleed linemay further be automated or manually operated.

[0062] The filter support structure may be made of any suitablematerials and may have any suitable configuration for supporting anynumber of filter housing assemblies and valve assemblies. The filtersupport structure may further include any number of inlet and outletpassages and filter input and filter output channels to correspond withfilter housing assemblies attached to the filter support structure.

[0063] The valve assembly may be made of any suitable materials and mayhave any suitable configuration for supporting a movable valve on or inthe filter support structure while maintaining a fluid tightrelationship therebetween. The valve of the valve assembly may bemanipulated in any suitable manner to achieve any number of suitablevalve positions for diverting fluid flow within the system. For example,instead of a slide valve, the valve assembly may include a spool valveor a disc valve to divert polymer fluid from at least one filter housingassembly to another. The valve assembly may further include any suitablevalve position indicator and may be automated or manually operated.

[0064] The dimensioning and spacing of the elongated apertures for thefilter input and output channels as well as the corresponding groovesfor the valve may have any suitable dimensions as well as any suitablespacing arrangement with respect to each other to facilitate fluidcommunication with the valve at varying valve positions. For example,intermediate valve positions as described above may be obtained byvarying the dimensions and spacing of the grooves on the valve ratherthan providing shorter dimensions for the elongated apertures of thefilter output channels in comparison with the elongated apertures of thefilter input channels on the main block upper surface.

[0065] The filter housing assemblies, valve assembly and filter supportstructure may include any number of heating elements having any suitableconfigurations and disposed at any suitable, locations on or in thosesystem components. The heating elements of the system may further bemonitored and controlled by a single controller or a plurality ofcontrollers.

[0066] The filtration system of the present invention is useful infiltering molten polymer fluids as well as polymer solutions in suitablesolvents in a variety of textile or other applications. It is furthernoted that the system of the present invention is not limited tofiltering polymer fluids but is capable of filtering many differenttypes of fluids in a continuous process.

[0067] Having described preferred embodiments of a filtration systemutilizing a single valve to direct fluid streams between filter housingassemblies, it is believed that other modifications, variations andchanges will be suggested to those skilled in the art in view of theteachings set forth herein. It is therefore to be understood that allsuch variations, modifications and changes are believed to fall withinthe scope of the present invention as defined by the appended claims.

What is claimed is:
 1. A continuous fluid filtration system comprising:a filter support including an inlet passage to receive fluid enteringsaid system and an outlet passage to deliver filtered fluid out of saidsystem; a first filter housing assembly and a second filter housingassembly connected to said filter support, each filter housing assemblyincluding a chamber disposed therein, filter media disposed within saidchamber, an input port to deliver fluid into said chamber and an outputport to deliver filtered fluid out of said chamber, wherein said inputand output ports are disposed on a housing head at one end of eachfilter housing assembly; and a valve to selectively alternate fluid flowbetween said first and second filter housing assemblies by establishingfluid communication between said inlet passage and one of said inputports of said first and second filter housing assemblies and betweensaid outlet passage and a corresponding one of said output ports of saidfirst and second filter housing assemblies.
 2. The system of claim 1,wherein said valve is adjustable to an intermediate position permittingfluid flow to said first and second filter housing assemblies from saidinlet passage while preventing fluid flow from one of said first andsecond filter housing assemblies to said outlet passage.
 3. The systemof claim 1, wherein said valve is adjustable to a plurality of valvepositions that vary fluid flow within said system, and each valveposition to which said valve is adjustable permits fluid flow into andout of at least one of said first and second filter housing assemblies.4. The system of claim 1, wherein said valve includes an engagingsurface that engages a first surface of said filter support, and saidvalve is slidably displaced along said first surface to selectivelyalternate fluid flow between said first and second filter housingassemblies.
 5. The system of claim 4, wherein said housing headincluding said input and output ports for each of said first and secondfilter housing assemblies engages a second surface of said filtersupport, and said filter support includes a plurality of filter inputchannels and a plurality of filter output channels extending within saidfilter support and emerging from said filter support at said secondsurface, each input port of said first and second housing assemblies isin fluid communication with a corresponding filter input channel andeach output port of said first and second filter housing assemblies isin fluid communication with a corresponding filter output channel. 6.The system of claim 5, wherein said filter input channels and saidfilter output channels emerge from said first surface of said filtersupport, said valve includes an inlet groove and an outlet groovedisposed on said engaging surface, and said valve selectively alternatesfluid flow between said first and second filter housing assemblies byaligning said inlet groove and said outlet groove on said second surfacesuch that said inlet groove is in fluid communication with said inletpassage and one of said filter input channels and said outlet groove isin fluid communication with said outlet passage and one of said filteroutput channels.
 7. The system of claim 1, wherein each filter housingassembly includes a bleed line to release air entrapped within saidchamber of said filter housing assembly.
 8. The system of claim 1,wherein said filter media within said chamber of each filter housingassembly comprises a plurality of candle filters.
 9. The system of claim8, wherein each candle filter of each filter housing assembly receivespolymer fluid entering said chamber from said input port and each filterhousing assembly further includes a passage in fluid communication withsaid plurality of candle filters to deliver filtered polymer fluid fromsaid plurality of candle filters to said output port.
 10. The system ofclaim 1, wherein each filter housing assembly includes a heating elementto maintain each filter housing assembly at a desired temperature. 11.The system of claim 10, wherein each heating element comprises a heatingjacket surrounding an exterior surface portion of a corresponding filterhousing assembly.
 12. The system of claim 11, wherein each heatingjacket includes a temperature sensor to detect the temperature of saidcorresponding filter housing assembly, and said temperature sensor andsaid heating jacket are in communication with a controller that controlsthe temperature of said heating jacket based upon a temperature measuredby said temperature sensor.
 13. The system of claim 1, wherein saidfilter support and said valve each include a heating element to maintainsaid filter support and said valve at desired temperatures.
 14. Thesystem of claim 1, wherein each filter housing assembly further includesa housing removably secured to said housing head, said housing includingsaid chamber disposed therein, and said housing head is configured toreceive a plurality of different sized housings having different chambervolumes to accommodate varying fluid filtering capacities.
 15. Acontinuous fluid filtration system comprising: at least one set of atleast two filter housing assemblies, each filter housing assemblyincluding a chamber disposed therein, filter media disposed within saidchamber, an input port to deliver fluid into said chamber and an outputport to deliver filtered fluid out of said chamber, wherein said inputand output ports are disposed on one end of each filter housingassembly; a filter support including at least one inlet passage and atleast one outlet passage corresponding to each set of at least twofilter housing assemblies, wherein each inlet passage receives fluidentering said system and each outlet passage delivers filtered fluid outof said system; and a valve to selectively alternate fluid flow betweenfilter housing assemblies in at least one selected set of at least twofilter housing assemblies by establishing fluid communication between aninlet passage corresponding to said at least one selected set and aninput port of a filter housing assembly of said at least one selectedset and an outlet passage corresponding to said at least one selectedset and an output port of a filter housing assembly of said at least oneselected set.
 16. A continuous fluid filtration system comprising: aplurality of filter housing assemblies, each filter housing assemblyincluding a plurality of filter elements, an input port to deliver fluidinto said filter housing assembly and an output port to deliver fluidout of said filter housing assembly; a filter support to support saidfilter housing assemblies, said filter support including an inletpassage to receive fluid entering said system and an outlet passage todeliver filtered fluid out of said system; and a valve assembly toselectively alternate fluid flow between a first filter housing assemblyand a second filter housing assembly by establishing fluid communicationbetween said inlet passage and one of said input ports of said first andsecond filter housing assemblies and between said outlet passage and acorresponding one of said output ports of said first and second filterhousing assemblies, wherein said valve assembly is adjustable to createa plurality of fluid flow paths within said system, and any fluid flowpath created by said valve assembly includes an exit to said outletpassage through at least one of said first and second filter housingassemblies.
 17. A method of continuously filtering fluid in a filtrationsystem including a plurality of filter housing assemblies supported by afilter support and a valve to alternate fluid flow between said filterhousing assemblies, said filter support including an inlet passage todeliver fluid into said system and an outlet passage to deliver filteredfluid out of said system, and each filter housing assembly including aninput port and an output port disposed at an end that is connected tosaid filter support and a chamber disposed within said filter housingassembly, wherein said chamber includes filter media and is in fluidcommunication with said input and output ports, the method comprising:(a) manipulating said valve to establish fluid communication betweensaid inlet passage and said input port of a first filter housingassembly and between said outlet passage and said output port of saidfirst filter housing assembly; and (b) delivering fluid to said inletpassage to force said fluid to pass through said input port, travel intosaid chamber, pass through said filter media and exit said output portof said first filter housing assembly to exit said system via saidoutlet passage as filtered fluid.
 18. The method of claim 17, furthercomprising: (c) subsequent to (a) and (b), further manipulating saidvalve to establish fluid communication between said inlet passage andsaid input port of a second filter housing assembly while maintainingfluid communication between said inlet passage and said input port ofsaid first filter housing assembly and between said outlet passage andsaid outlet port of said first filter housing assembly.
 19. The methodof claim 18, further comprising: (d) subsequent to (c), bleedingentrapped air from said chamber of said second filter housing assembly;(e) subsequent to (d), manipulating said valve to maintain fluidcommunication between said inlet passage and said input port of saidsecond filter housing assembly and establish fluid communication betweensaid outlet passage and said output port of said second filter housingassembly while simultaneously terminating fluid communication betweensaid inlet passage and said input port of said first filter housingassembly and between said outlet passage and said outlet port of saidfirst filter housing assembly.
 20. The method of claim 19, furthercomprising: (f) subsequent to (e), removing said first filter housingassembly from said filter support.
 21. The method of claim 17, whereinan engaging surface of said valve engages said filter support and saidvalve includes a first groove and a second groove disposed on saidengaging surface, and (a) includes: (a.1) sliding said valve along saidfilter support to establish fluid communication between said firstgroove, said inlet passage and said input port of said first filterhousing assembly and between said second groove, said outlet passage andsaid output port of said first filter housing assembly.
 22. The methodof claim 17, further comprising: (c) heating said first filter housingassembly to a desired temperature.
 23. The method of claim 22, wherein(c) includes: (c.1) measuring a temperature of said first filter housingassembly; and (c.2) controlling the heating of said first filter housingassembly based upon the measured temperature.
 24. The method of claim17, further comprising: (c) heating said filter support and said valveto desired temperatures.
 25. A method of diverting fluid flow in afiltration system between a first filter housing assembly and a secondfilter housing assembly comprising: (a) passing fluid through said firstfilter housing assembly, wherein fluid flows into and out of said firstfilter housing assembly at one end of said first filter housingassembly; and (b) diverting fluid flow within said system from saidfirst filter housing assembly to said second filter housing assembly.26. The method of claim 25, wherein (b) includes: (b.1) manipulating aslide valve to divert fluid flow within said system from said firstfilter housing assembly to said second filter housing assembly.
 27. Acontinuous fluid filtration system comprising: a plurality of means forfiltering fluid, each means for filtering including an input port todeliver fluid into said means for filtering and an output port todeliver filtered fluid out of said means for filtering, wherein saidinput port and said output port are disposed on an end of each means forfiltering; a means for supporting said plurality of means for filtering,said means for supporting including a means for delivering fluid to andreceiving filtered fluid from each filtering means; and a means fordiverting and selectively alternating fluid flow between a first meansfor filtering and a second means for filtering of said plurality ofmeans for filtering by establishing fluid communication between saidmeans for delivering of said means for supporting and the inlet andoutlet ports of one of said first and second means for filtering. 28.The system of claim 27, wherein said means for diverting is adjustablefor permitting fluid flow from said means for delivering to said inletport of each of said first and second means for filtering whilepreventing fluid flow from one of said first and second means forfiltering to said means for delivering.
 29. The system of claim 27,wherein said means for diverting is adjustable to provide a plurality ofdifferent fluid flow paths within said system, and each fluid flow pathexits said system from at least one means for filtering through saidmeans for delivering.
 30. The system of claim 27, wherein each of saidmeans for filtering includes a means for heating said means forfiltering to a desired temperature.
 31. The system of claim 27, whereineach of said means for diverting and said means for supporting includesa means for heating said means for diverting and said means forsupporting to a desired temperature.